The purpose of the proposed research is to determine the detailed mechanism by which O2 oxidoreductases catalyze reactions of molecular oxygen. Since many O2 oxidoreductases are involved in defects of metabolism it is hoped that a greater understanding of their mechanisms will aid in the control or alleviation of such metabolic diseases. Two specific enzymes being investigated are pig kidney inositol oxygenase and pig liver 4-hydroxyphenylpyruvate dioxygenase. In addition, some model reactions for various oxidases and oxygenases are being studied. The methods to be used are those which have been proved so successful in arriving at a greater understanding of non-redox enzymic reactions. They will include: kinetic methods, isotope tracer studies, use of inactivators and modified substrate molecules, EPR techniques, etc.